The present invention relates to an apparatus for detecting a voltage and more particularly to a portable type voltage detector generally called as a lineman's detector.
Hithertofore several types of the voltage detectors have been known. The most widely used voltage detector is of a neon tube type which comprises a probe made of electrically conductive material, a casing made of electrically insulating material and having embedded therein a rear portion of the probe and a neon tube having one terminal connected to the rear end of the probe. When the exposed front portion of the probe is made contact with an electrically conductive member to which a voltage is applied, a current flows through the probe, neon tube and a body of a user to the ground and the neon tube is fired, so that the user can detect a fact that the voltage is applied to the electrically conductive member to which the probe is touched. This type of voltage detector can be manufactured very easily and is small in size and light in weight, and thus has been widely used as the lineman's detector. However by means of this type of voltage detector it is impossible to detect a voltage with interposing an electrical insulator between the conductor and the probe. For example, when the probe is made contact with an electrically insulating coating or sheath of an electric wire, the neon tube does not fire even if a voltage is applied to a core conductor surrounded by the insulating coating. It is very convenient and is sometimes required to detect the voltage applied to the core conductor without directly contacting the probe to the core conductor. An amplification type voltage detector has been also known, but this type of voltage detector is used for a rather high voltage and is very large in size and heavy in weight and thus is not suitable as the portable type lineman's detector. Moreover the sensitivity of this detector for low voltage from several tens voltage to several hundreds voltage is very low and the voltage cannot be detected with interposing the insulating material.